Liquid crystalline polyester and its preparation method and application

Abstract

The application discloses a liquid crystal polyester and a preparation method and application thereof, wherein the amount of a repeating unit (I) is 24.1mol% to 77mol% based on the total amount of the repeating units, the repeating unit (I) has a phenylene structure; and the amount of a repeating unit (II) is 23mol% to 75.9mol%, the repeating unit (II) has a naphthalene structure. The liquid crystal polyester provided by the application has very low dielectric constant and dielectric loss, and the processability and flexibility of the liquid crystal polyester film are improved, and the non-uniformity of the appearance and dielectric properties of the liquid crystal polyester film caused by blending of aliphatic polyester additives is avoided.

Description

Technical Field

[0001] This invention relates to the field of special engineering plastics technology, specifically to a liquid crystal polyester, its preparation method, and its application. Background Technology

[0002] Flexible copper-clad laminates (CCLs) are widely used in the electronics and electrical manufacturing industry due to their combination of thinness and excellent flexibility, which meets the requirements for miniaturization and weight reduction of equipment and enables continuous mounting of components. Furthermore, the high-frequency signal transmission of 5G communication technology places even higher demands on the dielectric constant and dielectric loss performance of the insulating substrate of flexible CCLs.

[0003] Thermoplastic liquid crystal polyester film, due to its extremely low dielectric constant and dielectric loss, can well meet the needs of high-frequency signal transmission in 5G communication technology as an insulating substrate for flexible copper-clad laminates. However, due to its flow characteristics, general thermoplastic liquid crystal polyester is difficult to meet the requirements for blow molding film manufacturing, and polyester additives are usually added to improve its processability for blow molding.

[0004] Meanwhile, to meet the requirements of miniaturization and thinning of terminal devices, flexible copper-clad laminates also need to meet the complex design requirements of multi-layered three-dimensional structures. Therefore, the thermotropic liquid crystal polyester film, as an insulating substrate, also needs to exhibit good flexibility. However, due to its rigid molecular chain structure, thermotropic liquid crystal polyester typically performs poorly in terms of flexibility. In existing published technical solutions, the flexibility of the thermotropic liquid crystal polyester film is generally improved by adding polyester additives.

[0005] The above-mentioned technical methods, on the one hand, can easily lead to a decrease in the thermal stability of thermoplastic liquid crystal polyester, making it difficult to meet the temperature requirements of the mounting and soldering process for reliable connection of complex three-dimensional electronic components. On the other hand, the added aliphatic polyester additives can easily lead to a decrease in the uniformity of the appearance and dielectric properties of the thermoplastic liquid crystal polyester film due to insufficient blending reaction, thus affecting the accuracy of signal transmission. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention proposes a liquid crystal polyester and its preparation method. The liquid crystal polyester provided by this invention possesses extremely low dielectric constant and dielectric loss (dielectric constant between 3.0 and 3.8, dielectric loss between (1-1.21) × 10⁻⁶). -3 Within this range, the processability and flexibility of its blown film are improved, avoiding the inhomogeneity of appearance and dielectric properties of thermoplastic liquid crystal polyester films caused by blending aliphatic polyester additives.

[0007] Specifically, this is achieved through the following technical solutions:

[0008] A liquid crystal polyester, wherein the amount of repeating unit (I) is 24.1 mol%-77 mol%, and the repeating unit (I) has a phenylene structure; and the amount of repeating unit (II) is 23 mol%-75.9 mol%, and the repeating unit (II) has a naphthylene structure.

[0009] Preferably, based on the total amount of repeating units, the amount of repeating unit (I) is 41 mol%-60 mol%, and the amount of repeating unit (II) is 40 mol%-59 mol%.

[0010] Preferably, when the molar ratio of phenylene to naphthylene is 0.7 to 1.5, the dielectric constant of the liquid crystal polyester is smaller and the dielectric loss is lower.

[0011] Furthermore, the liquid crystal polyester is obtained by reacting aromatic diphenol monomers, aromatic hydroxycarboxylic acids, and aromatic dicarboxylic acid monomers under catalytic conditions; the aromatic diphenol monomer has the structural formula HO-Ar1-OH, the aromatic hydroxycarboxylic acid has the structural formula HO-Ar2-COOH, and the aromatic dicarboxylic acid monomer has the structural formula HOOC-Ar3-COOH.

[0012] Preferably, Ar1, Ar2, and Ar3 are each independently 1,4-phenylene, 1,3-phenylene, 1,2-phenylene, 2,7-naphthylene, 2,6-naphthylene, 2,5-naphthylene, 2,2'-biphenylene, 2,3'-biphenylene, 2,4'-biphenylene, 3,3'-biphenylene, or 3,4'-biphenylene, but not all of Ar1, Ar2, and Ar3 are 1,4-phenylene. Among them, 1,3-phenylene, 1,2-phenylene, 2,7-naphthylene, 2,6-naphthylene, 2,5-naphthylene, 2,2'-biphenylene, 2,3'-biphenylene, 2,4'-biphenylene, 3,3'-biphenylene, or 3,4'-biphenylene are repeating units with a "bending effect". The original liquid crystal polyester structure contains long and continuous p-phenyl-substituted monomer repeating units (i.e., 1,4-phenylene) in a rod-like structure. By introducing an appropriate amount of repeating unit structural components with a "bending effect" into the liquid crystal polyester molecular chain structure, the rod-like structure of the molecular chain structure is appropriately disrupted, enhancing the inter-chain entanglement during melt flow, increasing the tensile viscosity of the thermotropic liquid crystal polyester melt, and improving the processability of blown film.

[0013] More preferably, Ar1, Ar2 and Ar3 are each independently 1,4-phenylene, 1,3-phenylene, 2,7-naphthylene or 2,6-naphthylene.

[0014] The Ar1 may be selected from one or more of 1,4-phenylene, 1,3-phenylene, 2,7-naphthylene, or 2,6-naphthylene.

[0015] The Ar2 may be selected from one or more of 1,4-phenylene, 1,3-phenylene, 2,7-naphthylene, or 2,6-naphthylene.

[0016] The Ar3 may be selected from one or more of 1,4-phenylene, 1,3-phenylene, 2,7-naphthylene, or 2,6-naphthylene.

[0017] Furthermore, the catalyst is a Lewis acid catalyst. Lewis acids, also known as electron docking acceptors, can accept electron pairs because their valence orbitals lack electron pairs. Therefore, a Lewis acid catalyst possesses the property of accepting electron pairs. Using a Lewis acid catalyst, a branched structure is introduced through an isomerization reaction. After the film is formed, the aryl groups on the short branches of different molecular chains form a weak physical "crosslinking" effect through π-π interactions, thereby improving the flexibility of the film.

[0018] Branched structures refer to structures formed by the Fries rearrangement of molecular chains during a reaction. The specific reaction mechanism is as follows:

[0019] .

[0020] Further, the catalyst is one of potassium bicarbonate, calcium bicarbonate, sodium bicarbonate, lithium acetate, cesium acetate, ferrous acetate, magnesium bicarbonate, zinc acetate, lead carbonate, ammonium acetate, aluminum trichloride, boron trifluoride, ferric bromide, or lanthanum trifluoromethanesulfonate, preferably potassium bicarbonate, sodium bicarbonate, calcium bicarbonate, lithium acetate, cesium acetate, magnesium bicarbonate, zinc acetate, lead carbonate, or ferrous acetate.

[0021] Furthermore, the melt tensile viscosity of the liquid crystal polyester is 3000-6000 Pa·s, the dielectric constant of the liquid crystal polyester is 3-5, and the dielectric loss tangent is 1×10⁻⁶. -3 -3×10 -3 The tensile modulus of the film made from the liquid crystal polyester is 3-6 GPa. The tensile modulus of the film is tested according to ASTM D882-2018 standard. The dielectric constant is measured at room temperature using a vector network analyzer. The dielectric loss is also measured at room temperature using a vector network analyzer. The test sample is a 1 mm thick liquid crystal polyester sheet, and the measurement frequency is 2.5 GHz.

[0022] The present invention also provides a method for preparing the above-mentioned liquid crystal polyester, comprising the following steps:

[0023] S1: Under inert gas pressure, aromatic diphenol monomers and aromatic hydroxycarboxylic acids undergo acylation reaction in the presence of an acylation agent; wherein the acylation agent is acetic anhydride, propionic anhydride or butyric anhydride.

[0024] S2: After the acylation reaction is completed, the pressure is reduced to normal pressure, aromatic dicarboxylic acid monomer and catalyst are added, and the mixture is melt-condensed after heating to obtain the prepolymer;

[0025] S3: Cool and solidify the prepolymer from step S2 and granulate it, then perform solid-state polymerization to obtain the liquid crystal polyester.

[0026] More specifically, it includes the following steps:

[0027] S1: Under inert gas pressure, acylation reaction is carried out using hydroxy aromatic carboxylic acid monomers and aromatic diphenols as raw materials and an acylation agent. The pressure is maintained at 0.1MPa-0.2MPa, the reaction temperature is 100℃-180℃, and the reaction time is 30 minutes-10 hours.

[0028] S2: After the acylation reaction is completed, the pressure inside the reactor is reduced to atmospheric pressure, the catalyst and aromatic dicarboxylic acid are added, and the temperature is increased to 200℃-400℃ at a rate of 0.1℃ / min-150℃ / min. Acetic acid and unreacted acetic anhydride molecules are discharged from the distillation column. When the amount of acetic acid received reaches more than 90% of the theoretical value, the temperature is kept constant at 300-400℃ for 5-30 minutes. The pressure inside the reactor is reduced to 0.1-10 kPa. This pressure reduction condition is maintained and the reaction system is programmed to be heated to the maximum reaction temperature. The prepolymer is obtained by melt polycondensation.

[0029] S3: Cool and solidify the prepolymer and granulate it. Then carry out solid-state polymerization in a solid-state polymerization container to obtain liquid crystal polyester particles. The vacuum degree is 0.1Pa-50kPa, the solid-state polymerization temperature is 160-340℃, and the reaction time is 0.5 hours-40 hours.

[0030] Furthermore, the inert gas is nitrogen, argon, or carbon dioxide, and using an inert gas can suppress the occurrence of side reactions.

[0031] The present invention also provides the application of the above-mentioned liquid crystal polyester in molding films, which can be used to prepare flexible copper-clad laminates, high-strength fibers and high-strength sheets, especially for the preparation of flexible copper-clad laminates.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] By introducing unit structures with a "bending effect" into the molecular chain structure of liquid crystal polyester, and appropriately disrupting the rod-like structure of the molecular chain, interchain entanglement is enhanced during melt flow, increasing the tensile viscosity of the thermotropic liquid crystal polyester melt and improving the processability of blown films. Using a catalyst with Lewis acidity, branching is introduced through an isomerization reaction. After film formation, the aryl groups on the short branches of different molecular chains form weak physical "crosslinking" through π-π interactions, improving the flexibility of the film. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] <Preparation of Examples and Comparative Examples>

[0036] The raw materials used in the embodiments and comparative examples of this invention are all commercially available.

[0037] The methods for preparing liquid crystal polyester in the embodiments and comparative examples of the present invention are as follows:

[0038] S1: Under nitrogen pressure, acylation reaction is carried out using hydroxy aromatic carboxylic acid monomers and aromatic diols as raw materials and an acylation agent. The pressure is maintained at 0.1MPa-0.2MPa, the reaction temperature is 100℃-180℃, and the reaction time is 30 minutes-10 hours.

[0039] S2: After the acylation reaction is completed, the pressure inside the reactor is reduced to atmospheric pressure, the catalyst and aromatic dicarboxylic acid are added, and the temperature is increased to 200℃-400℃ at a rate of 0.1℃ / min-150℃ / min. Acetic acid and unreacted acetic anhydride molecules are discharged from the distillation column. When the amount of acetic acid received reaches more than 90% of the theoretical value, the temperature is kept constant at 300-400℃ for 5-30 minutes. The pressure inside the reactor is reduced to 0.1-10 kPa. This pressure reduction condition is maintained and the reaction system is programmed to be heated to the maximum reaction temperature. The prepolymer is obtained by melt polycondensation.

[0040] S3: Cool and solidify the prepolymer and granulate it. Then carry out solid-state polymerization in a solid-state polymerization container to obtain liquid crystal polyester particles. The vacuum degree is 0.1Pa-50kPa, the solid-state polymerization temperature is 160-340℃, and the reaction time is 0.5 hours-40 hours.

[0041] Methods for preparing thin films from liquid crystal polyesters in the examples and comparative examples:

[0042] There are no specific limitations; the film can be prepared by a T-die method, in which molten liquid crystal polyester is extruded and wound up using a T-die; or by a blown film-forming method, in which molten resin is extruded into a cylindrical shape using an extruder equipped with a ring die, cooled, and wound up; or by a method that obtains a film preform through hot pressing or solvent casting and then further stretches it into a film. To avoid disrupting the orientation of the liquid crystal polyester, the blown film-forming method is preferred.

[0043] Using a single-screw extruder, the liquid crystal polyester is heated and compounded at 5-30°C above its melting point, and then extruded at a speed of 500-1000 seconds. -1 The die shearing speed is adjusted so that the liquid crystal polyester film is obtained by melt extrusion from an annular blow molding die with a die diameter of 30-50 mm and a die gap of 1-2 mm, under the condition of a blow-up ratio of 3.8-5.2.

[0044] <Test Standards>

[0045] The performance testing standards for the various embodiments and comparative examples of this invention are as follows:

[0046] Thermotropic liquid crystallization: Use a hot-stage polarizing microscope to observe whether the liquid crystal polyester above the melting point has birefringence. If it does, it has thermotropic liquid crystallization; if not, it does not have thermotropic liquid crystallization.

[0047] Melt tensile viscosity: The test standard is ISO 20965-2005, measured using a capillary rheometer, combined with the classic Cogswell test method. The test temperature is selected to be 20°C above the melting point, and a long die with an inner diameter of 1 mm and a length of 20 mm is used at a strain rate of 10 s⁻¹. -1 Time measurement;

[0048] Tensile modulus: Tested using a universal testing machine. The test sample was a film prepared from liquid crystal polyester as described in the examples and comparative examples, with dimensions of 50 μm × 10 mm × 15 cm. The test method was in accordance with ASTM D882-2018.

[0049] Dielectric constant: The test standard is IEC 60250, and the measurement is performed at room temperature using a vector network analyzer; the test sample is a 100*100*1.8mm liquid crystal polyester sheet, and the dielectric constant is tested at a frequency of 2.5GHz according to the IEC 60250 test standard, and the test temperature is 23℃.

[0050] Dielectric loss tangent: Measured using a vector network analyzer at room temperature; the test sample was a 100*100*1.8mm liquid crystal polyester sheet, and the dielectric constant was tested at a frequency of 2.5GHz according to the IEC 60250 test standard at a test temperature of 23℃.

[0051] Film-forming properties: The liquid crystal polyester is heated and melted using a uniaxial extruder with the barrel temperature set at the melting point of the liquid crystal polyester. The resulting melt is then extruded through an annular die with a diameter of 30–60 mm and a gap of 0.5–1.5 mm, at a die temperature of 10–30 °C above the melting point, at a shear rate of 500–2000 s. -1Extruded above a die, the film expands and cools at a blow molding ratio of 1:7 to 1:4 and a stretching ratio of 2:1 to 6:1, and is then pulled out using rollers to obtain a liquid crystal polyester film with a thickness of 25 to 50 μm. Film continuity is judged based on the length of the continuous film: +++ indicates excellent blown film continuity (>400 meters); ++ indicates good blown film continuity (200 meters < 400 meters); + indicates acceptable but average blown film continuity (<200 meters); - indicates no blown film formation possible; -* indicates no blown film formation possible and cannot be tested.

[0052] Table 1. Composition (mol%) of liquid crystal polyester monomers and test results of various properties in the examples

[0053]

[0054]

[0055] Table 2. Comparative examples of liquid crystal polyester monomer composition (mol%) and test results of various properties.

[0056]

[0057]

[0058] If the tensile modulus of a material is too high, its flexibility will decrease; if the tensile modulus is too low, it will be easily deformed; if the tensile viscosity is too high, it will be impossible to inflate; if the tensile viscosity is too low, the film bubble will easily rupture. Both of these need to be within a suitable range to achieve good film-forming properties.

[0059] In Comparative Examples 1 and 3, the inappropriate molar ratio of phenylene and naphthylene structures will result in no thermotropic liquid crystal properties and poor film-forming properties.

[0060] Comparative Example 2, because all the repeating units are phenylene structures, although it has thermotropic liquid crystal properties, it cannot be used for blow molding and has poor film-forming properties.

[0061] Compared with Example 1, Comparative Example 4 did not use a catalyst with Lewis acidity. Although Comparative Example 5 also had thermotropic liquid crystal properties, its film-forming properties were poor and it could not be blow-molded into a film.

[0062] In Comparative Example 5, all the repeating units were naphthyl-based structures, which caused them to solidify during the polymerization process and make them unsuitable for blow molding.

[0063] Example 8

[0064] Using a single-screw extruder, the liquid crystal polyester of Example 2 was heated and compounded at 5-30°C above its melting point, and then subjected to a process of 500-1000 seconds. -1The liquid crystal polyester film was obtained by melt extrusion from an annular blow molding die with a die diameter of 30-50 mm and a die gap of 1-2 mm at a shear rate of 3.8-5.2 under the condition of a blow-up ratio of 3.8-5.2. The test results were as follows: tensile viscosity of 5054 Pa·s, tensile modulus of 3.8 GPa, dielectric constant of 3.80, and dielectric loss tangent of 1.86 × 10⁻⁶. -3 The film-forming properties are characterized by good blown film continuity, indicating that it also possesses a low dielectric constant, a low dielectric loss tangent, and good blown film processability and flexibility. Therefore, it can be considered that the liquid crystal polyester provided by this invention is suitable for films with high requirements for dielectric constant, dielectric loss tangent, blown film processability, and flexibility, such as flexible copper-clad laminates, high-strength fibers, and high-strength sheets, especially flexible copper-clad laminates.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A liquid crystalline polyester, characterized in that, Based on the total amount of repeating units, the amount of repeating unit (I) is 41 mol%-77 mol%, and repeating unit (I) has a phenylene structure; the amount of repeating unit (II) is 23 mol%-59 mol%, and repeating unit (II) has a naphthylene structure; The liquid crystal polyester is obtained by reacting aromatic diphenol monomers, aromatic hydroxycarboxylic acids, and aromatic dicarboxylic acid monomers under catalytic conditions; the catalyst is a Lewis acid catalyst. The aromatic diphenol monomer has the structural formula HO-Ar1-OH, the aromatic hydroxycarboxylic acid has the structural formula HO-Ar2-COOH, and the aromatic dicarboxylic acid monomer has the structural formula HOOC-Ar3-COOH. Ar1, Ar2 and Ar3 are each independently 1,4-phenylene, 1,3-phenylene, 1,2-phenylene, 2,7-naphthylene, 2,6-naphthylene, and 2,5-naphthylene, but not all of Ar1, Ar2 and Ar3 are 1,4-phenylene.

2. The liquid crystalline polyester according to claim 1, characterized in that Based on the total amount of repeating units, the amount of repeating unit (I) is 41 mol%-60 mol, and the amount of repeating unit (II) is 40 mol%-59 mol.

3. The liquid crystalline polyester of claim 1, wherein The molar ratio of the repeating unit (I) to the repeating unit (II) is 0.7-1.

5.

4. The liquid crystalline polyester of claim 1, wherein Ar1, Ar2 and Ar3 are each independently 1,4-phenylene, 1,3-phenylene, 2,7-naphthylene or 2,6-naphthylene.

5. The liquid crystalline polyester of claim 1, wherein The catalyst is one of potassium bicarbonate, calcium bicarbonate, sodium bicarbonate, lithium acetate, cesium acetate, ferrous acetate, magnesium bicarbonate, zinc acetate, lead carbonate, ammonium acetate, aluminum trichloride, boron trifluoride, ferric bromide, or lanthanum trifluoromethanesulfonate.

6. The liquid crystalline polyester of claim 5, wherein The catalyst is one of potassium bicarbonate, sodium bicarbonate, calcium bicarbonate, lithium acetate, cesium acetate, magnesium bicarbonate, zinc acetate, lead carbonate, or ferrous acetate.

7. The liquid crystalline polyester according to claim 1 or 2, characterized in that The melt extensional viscosity of the liquid crystalline polyester is 3000-6000 Pa-s, the dielectric constant is 3-5 and the dielectric loss tangent is 1 x 10 -3 -3 x 10 -3 -3.

8. A process for the preparation of a liquid crystalline polyester according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Under inert gas pressure, aromatic diphenol monomers and aromatic hydroxycarboxylic acids undergo an acylation reaction in the presence of an acylating agent; S2: After the acylation reaction is completed, the pressure is reduced to normal pressure, aromatic dicarboxylic acid monomer and catalyst are added, and the mixture is melt-condensed after heating to obtain the prepolymer; S3: The prepolymer from step S2 is cooled, solidified, and granulated, and then subjected to solid-state polymerization to obtain the liquid crystal polyester.

9. The application of the liquid crystal polyester according to any one of claims 1-7 in the molding of films, particularly in the preparation of flexible copper-clad laminates, high-strength fibers and high-strength sheets.

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